With the introduction of packet-oriented technologies such as UMTS and GPRS, it is to be expected that data transmission will increasingly take place wirelessly in future. At the same time the data transmission will not be restricted to the transmission of voice information, but rather other services, such as those offered for example on the Internet, will increasingly be used wirelessly.
At the present time, most mobile radio networks are structured on a connection-oriented basis. This connection orientation is present at least between the terminal device and the base station. The backbone networks, in contrast, often have a packet-oriented structure. With voice and data transmissions in particular, however, the full bandwidth is not needed, since a data transmission takes place only at discrete instants in time and there is often a long time interval between the individual, actual information transmissions. Consequently a large portion of the bandwidth is wasted. Packet-oriented networks have the advantage that only the required bandwidth is used by packets. In this case, the data stream is split up into small packets. A disadvantage with this approach, however, is that in certain conditions of increased demand insufficient bandwidth is available. With voice transmissions in particular this leads to a considerable loss in quality which manifests itself in poor sound quality. Quality management is necessary for networks of this kind. It is also necessary that the data packets are routed faster through the network. In order to achieve this, high-speed switches and routers are required.
In order to cater for the increased data traffic with wireless subscribers in the future also, access networks for mobile radio networks will also be IP-based in future, i.e. there will be an IP-based transport network, referred to as the RAN (Radio Access Network), between the base stations and the gateway into the core network. Terminal devices set up a connection via an air interface initially to a base station BS which terminates the air interface. The data of the terminal device MH is then routed by means of an access router AR. Generally the interconnected access routers form the radio access network. The AR handles the forwarding of the data to the radio access server (RAS) or further routers.
Because of the different topologies of the networks a protocol tunnel is often set up between terminal device MH and access router RAS or between AR and RAS as well as between AR and AR. A protocol tunnel is always present when a first transmission protocol is encapsulated in a second transmission protocol. This is referred to as encapsulating the packets of a first transmission protocol into the packets of the second transmission protocol. This is always necessary, for example, if the first transmission protocol is not supported on a network segment. The packet must then be routed in this network segment with the aid of the second transmission protocol. The protocol tunnel provides a number of advantages.
For the terminal device, mobility can be supported transparently in the transport network RAN using any means. This advantage is based on the fact that the packets are not modified and consequently the type and form of the transport can be determined by the topology of the network without any risk of a modification of the user data.
Non IP-based data (e.g. compressed and/or encrypted IP packets, voice) can simply be routed via the transport network RAN to suitable converters at the edge of the transport network RAN, provided the tunnel technology used supports the transport of data packets of other protocols than IP.
Known methods use tunnels either from the terminal device MH to the RAS or from the access router AR to the RAS. Different technologies can be used for this, e.g. PPP, IP-in-IP.
Because of its simple structures and high performance, MultiProtocol Label Switching (MPLS, IETF Proposed Standard, [RFC3031]) can also be used advantageously as the tunnel technology. In MPLS networks a packet travels from one router to the next. Each router makes an independent decision with regard to the forwarding of packets. This means that each router analyzes the header of the packet and each router executes a program with the router algorithm. Each router selects a new route as a function of the result of the router algorithm. The selection of the next route is therefore done in two steps. The first step partitions the entire set of possible packets into a set of forwarding equivalence classes (FEC). The second step maps each FEC onto a route. As far as the decision on the forwarding is concerned, no distinction is made between the packets belonging to the same FEC. Different packets belonging to the same FEC cannot be differentiated. In this respect the present invention is different. In order to be able to use labels as addresses, a unique assignment to an FEC must exist. In other words, an FEC only ever comprises one label. This label is assigned to one destination address only.
Packets which have a different destination or source address are regarded as different packets. In order to be able to use MPLS for the present invention, however, a path and therefore the equivalence class must be unique. This means that an equivalence class stands for a unique source and destination terminal device or entity, and is further described below. In an MPLS network the assignment to an FEC is made only once, namely at the time the packet enters the network. The FEC to which a packet is assigned, is coded as a short value which is referred to as a label. When a packet is sent to the next route, the label is sent with it. No analysis of the further contents of the packet is performed at the following routers. Only the label is checked. The label is used as an index for a table from which the next route and the next label can be retrieved. The old label is replaced by the new label and the packet is forwarded to the next route. In an MPLS network forwarding is controlled only by means of the labels. This has a number of advantages. For example, the routers only need to have limited capabilities. They merely need to be able to analyze the label and check in a table which route is assigned to this label in order to replace the old label by a new label. Furthermore a high throughput can be achieved by these simple tasks. Further advantages can be found in [RFC 3031].
A few principles will be defined in the following. A label is a short, locally significant identifier which has a fixed length and is used to identify a FEC. The label serves to represent an FEC to which the packet is assigned. In the basic usage of the FEC this is assigned on the basis of the destination addresses of the network layer. In the original usage of the FEC it is not a coding of the network address, however. It is at this point, as detailed below, that the present invention makes a difference. As a result of the unique assignment of the label to a unique path it is equivalent to the coding of a network address.
In order to ensure that the routers assign the packets to the same equivalence classes, the routers regularly have to exchange information from which it is clear which packets are assigned to a label. It is also important that the same labels are not used by different routers, insofar as this makes a unique identification of the preceding router impossible. It should further be pointed out that upstreams and downstreams are handled differently. Thus, for example, these do not necessarily have the same labels. In the MPLS architecture the decision to bind a specific label to a specific equivalence class is made by the router which is located downstream in relation to this binding. The router which is downstream then informs the router which is upstream about this binding. This information can be transmitted for example as piggyback information on other packets.
In a further embodiment MPLS supports a hierarchy, whereby the processing of the packets provided with labels is totally independent of the level of the hierarchy. A packet which has no label can be regarded as a packet whose stack is empty. The use of the stack becomes clear when reference is made to the tunneling of packets. Tunneling of this kind is described in the document [RFC3031]. Packets are always tunneled when they are routed through a network path which lies between two routers, whereby this network path can, in turn, comprise a series of routers. If, for example, an explicit path was specified which comprises the routers R1 to R4, and if, between the routers R1 and R2, there lies a path which comprises the routers R1.1, R1.2, R1.3, then a further label is pushed onto the stack by the router R1. The routers R1.1, R1.2, R1.3 now operate on this new second element. As soon as the packet arrives at router R2, the topmost element is popped from the stack. It becomes problematical when there is no label on the stack. In the normal MPLS architecture the network address (normally the IP address) is analyzed in order to determine an equivalence class.
MPLS provides two types of route selection. The first type of route selection specifies the route already at the starting point. The individual routers which have to be passed through are determined. This entails a form of explicit routing. With hop-by-hop routing the routers are not specified explicitly, so each router can specify on the basis of its tables which is to be the next router. The present invention can be operated with both these methods of route selection.
Existing approaches to using MPLS are based on a use of MPLS in the interior of the network, for example between access router AR and RAS in the mobile radio network.
If the terminal device MH switches during ongoing operation from router ARx to router ARy, then it has to re-register with the access router (authentication). With this movement of the terminal device to a different base station or another access router, this tunnel is now switched to the current anchor point by means of signaling. Toward that end, however, this must be supported in different variations of the implementation in the access network IPv6 (IP version 6). As the mapping of such architectures onto existing IP backbones has revealed, a form of MPLS is mainly supported in this. IP networks are therefore implemented as overlay/VPN (Virtual Private Network) structures and their packets only switched quickly, which means less network load and overhead for router operation. In a tunneling of the information, however, an overhead does result in terms of the size of the information packets. IPv6 headers cause more than 40 bytes of header overhead at an average transport data size of 60 bytes (IPv6 incl. routing header), the user data of which in turn comprises only about 20 bytes (VoIP) [RFC 3031, RFC 2460]. Only 4 bytes are induced in each case by means of a shim header or MPLS header of, for example, MPLS. A shim header, also MPLS header, comprises further status and administrative information in addition to the label, which accounts for approx. 20 bits. Basically, a unique identification of the point-to-point link with its attributes, e.g. Quality of Service (QoS), and, of course, the identification of the respective bearer are required.
Known methods for reducing the overhead consist of a compute-intensive compression technique [RFC2507] (price-rohc-epic-00.txt [www.ietf.org/internet-drafts]) which the individual components or routers must support. These methods must manage the dynamic status during the connection, resulting in the consumption of a lot of resources (memory, CPU) and therefore imposing limits on the performance of the components. Where there are a great number of terminal devices (several thousand mobile handsets) which have to be served by a component, this can lead to an overloading of the system.
It should however be pointed out that the problems cited are not just restricted to networks which are operated with mobile terminal devices. Rather, this problem arises whenever different network topologies and architectures come into contact with one another and a tunneling of information packets becomes necessary. A limitation of the present invention to mobile radio networks is not intended.